The invention relates to a particle detector, making it possible in particular to detect high energy particles, allowing only little ionization.
It has been proposed for the purpose of replacing existing particle detectors, which are too complex and whose response is too slow, particularly when exposed to a very intense particle bombardment such as is possible with the new generation of particle accelerators, the use of the phenomenon of secondary electron emission by a thin porous material traversed by a beam of particles has been proposed. For this purpose, a target formed by an aluminium support plate covered by a thin porous layer of a material such as potassium chloride or cesium iodide having secondary electron emission characteristics which are particularly favourable with respect to the nature of the particles to be detected or discriminated in the case of a heterogeneous beam is placed in the beam of particles. A target of this type has the double advantage of not disturbing the beam of incident particles due to the low density of the material used and of supplying a rapid response due to the absence of inertia in the emitted secondary particles. However, due to the low density of the secondary electron emission material, the number of electrons emitted when the incident particles are at their ionization minimum is very low, despite the very good efficiency of this type of target. It is therefore indispensible to amplify the signal supplied by the target, i.e. to multiply the number of secondary electrons to the greatest possible extent. In practice, studies performed up to now in this type of detector have led to the use of conventional electron multipliers comprising for example several microchannel flat coils arranged in cascade between the target and an anode and polarized in an appropriate manner to accelerate the secondary electrons emitted between each of these flat coils. However, such an amplification device is not satisfactory, because it significantly reduces the efficiency of the detector and the amplification level obtained is not strictly proportional to the number of electrons emitted by the target, in view of the fact that the signals leaving the electron multipliers are often saturated.